Attention has recently been drawn to studies on organic semiconductor structures using an organic semiconductor material, and application of organic semiconductor structures to various devices has been expected. Devices utilizable, for example, in large-area flexible display devices, for example, thin-film transistors (also known as “organic TFTs”), luminescent elements, and solar cells are being studied for such application.
In order to utilize organic semiconductor structures on a practical level, the organic semiconductor layer formed of an organic semiconductor material should exhibit stable charge mobility in a wide service temperature range, and, at the same time, even thin film should be easily formed in a wide area. In particular, properties satisfying the following requirements are desired: the formation of a film by coating rather than film formation by conventional techniques such as vapor deposition is possible; properties in a film formation environment are stable; and stable high charge mobility can be exhibited in a wide service temperature range including room temperature (about −40 to +90° C.).
Regarding prior art documents relevant to the present invention, for example, non-patent document 1 describes an oligothiophene compound represented by the following chemical formula 3 as a nonlinear optical material. Non-patent possible and, thus, they are advantageous from the viewpoint of production. Further, the organic semiconductor layer formed using the organic semiconductor material is flexible and is highly mechanically stable and thus can be advantageously formed, for example, on a flexible plastic substrate.

The organic semiconductor layer formed of polythiophenes such as poly(3-hexylthiophene) represented by chemical formula a is disadvantageously likely to undergo oxidation by oxygen in the air exposed during film formation. TFT comprising an oxidized organic semiconductor layer suffers from a problem that the on/off ratio is reduced due to a rise in off current. To overcome this problem, for example, patent document 1 proposes poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene] represented by chemical formula b. The claimed advantage of this polymer material is that, since the polymer material is soluble in organic solvents, film formation using various coating and printing means is possible and, at the same time, the polymer material is less likely to undergo oxidation and can prevent a problem with oxidation.
Patent document 1: Japanese Patent Laid-Open No. 221434/2003